The present invention relates to a disk subsystem, and more particularly to an on-line dumping system and disk sub-system which perform high speed and high efficient dump processing without affecting on-line processing when dump processing for the magnetic disk sub-system is dumped.
In order to enhance the reliablity of a system of the magnetic disk sub-system, it is a common practice to dump data on another recording medium (such as a magnetic tape). Various techniques to reduce the amount of processing and enhance the performance of the dump processing have been proposed. For example, in a system disclosed in JP-A-57-90770, a disk controller stores position information of updated data blocks (such as tracks), and a higher rank unit dumps only the updated data blocks based on the above information in order to attain high efficient dumping.
On the other hand, in a large scale magnetic disk sub-system in which one controller controls a plurality of disk drives, while the controller services to one disk volume, an interruption by end of waiting of rotation for other disk volume is not accepted by the controller or the host unit.
The interruption by end of waiting of rotation means that the arrival of a head to a target position is reported to the higher rank unit and read/write is commanded to that record. If the controller or higher rank unit is in use at that time, a wait time for another rotation is required. A method for solving this problem is disclosed in JP-B-62-3455. In this method, when information is read from the disk drive and transferred to the higher rank unit, if the disk drive or the higher rank unit is in use and the coupling is not permitted when the interruption by end of waiting of rotation is issued, the content of the disk drive is written into a buffer memory provided for each disk drive, and when the disk controller or the higher rank unit is no longer in use, the information stored in the buffer is transferred to the disk controller.
JP-A-57-90770 aims at the reduction of the amount of dump, that is, the reduction of dump processing by operation, but does not pay consideration on the affect of the dump processing to the on-line processing. If the updated portion is small, the affect to the on-line processing will be small, but if a proportion of the updated portion between the previous dump processing and the start of the current dump processing is large, the affect of the dump processing on the on-line processing is material. In an extreme case, if all areas are updated, the entire data must be dumped.
In JP-B-62-3455, when the disk controller or the higher rank unit is busy and cannot accept the data transfer, the wait time for one rotation can be reduced. However, no consideration is paid to the dump processing for the track to be next processed. Further, as described above, no consideration is paid to the recognition of the on-line processing and the dump processing.